The reinforced composite industry has used reinforcing fibers, such as glass, mineral or polymeric fibers, in the form of continuous or chopped fibers, strands, and rovings for reinforcing a wide range of polymer compositions suitable for use in a wide range of applications. The reinforced products formed from such reinforced polymers may, in turn, be used in manufacturing a wide range of composite products that tend to exhibit improved resilience and strength relative to that which can be achieved with similar, but un-reinforced polymers and/or products. Such composite products may also be manufactured or processed in a manner sufficient to incorporate one or more decorative and/or functional elements into the products such as patterns, surface embossing, reinforcing structures and coloration.
Glass reinforced polyolefin composites are widely used in a variety of industries including, for example, automotive, construction, electrical, toys, sports equipment, appliances, and household furnishings. The use of a particular fiber and/or polymer(s) to manufacture a reinforced polyolefin may be guided by both the desired properties of the resulting composition to exhibit a particular combination of properties including, for example, mechanical, physical, chemical, and aesthetic properties.
The sizing compositions contribute to determining the final properties of the reinforced composite part. For example, during the manufacture of a composite part, and without tending to be bound to any particular theory or mechanism, it is believed that fiber size compositions form an interphase between the reinforcing fiber and the polymer matrix. When a load is applied to the composite part, force is transferred from the matrix to the fibers. The efficient transfer of this load and a good degree of adhesion between the fiber-interphase-polymer matrix is generally achieved by using an appropriate fiber size composition applied to the fibers.
Accordingly, there remains a need for a fiber size composition that can form an interphase that is strong, resistant to thermal degradation, resistant to chemical degradation, provides good adhesion between the fiber and fiber size composition, and provides good adhesion between the fiber size composition and the polymer matrix. Also, the fiber size composition must be compatible with both the reinforcing fibers, which may be inorganic, and the polymer matrix, which may be organic.
Inorganic compounds including sodium, potassium, and calcium tetraborates and sodium borohydride are reported in Japanese Kokai 10[1998]291841 (“JP '841”) and 10[1998]324544 (“JP '544”), the contents of which are incorporated herein, by reference, for all purposes and to the fullest extent both applicable and consistent with the disclosure provided below. These Japanese patent applications are generally directed to improving the performance of epoxy and urethane sizing compositions, but it is noted that epoxy resins tend to exhibit poor adhesion to the reinforcing fiber while polyurethanes, although having good adhesion to the reinforcing fiber, tends to adhere more poorly to the matrix resin. These patents do not, however, teach one of ordinary skill in the art how to improve the resistance of the final composites to discoloration. Further, these patents also do not teach or suggest the use of boron-fluorine compounds or other boron containing compounds in the sizing compositions.
In order to achieve composites with improved color and color stability, fiber size compositions preferably comprise thermally stable ingredients and/or supplemental additives that will tend to suppress oxidation of those components that are more susceptible to oxidation and discoloration. As used herein, the terms “size” and “sizing” refer to a composition applied to or a coating of such a composition provided on fibers for modifying the fiber surface characteristics over the entire length and fibers' performance by, for example, improving abrasion resistance during subsequent processing and/or promoting adhesion between the fibers and the polymeric materials to which they may be added as reinforcement.
While applying the sizing to the forming fibers that are gathered in bundles or strands some physical binding between filaments may occur and be present after drying, the sizing formulation can be selected in such a way that it promotes the dispersion of the sized fibers into the composite part. In fact, the sizing composition should be selected so as not to interfere or hinder to any significant degree the ability to disperse the sized fibers throughout the polymeric matrix. That is, the sizing should not tend to promote or increase agglomeration of the fibers, especially when such fibers are being incorporated into a polymeric matrix composition. This feature of the sizing compositions is in direct contrast to the effects of “binder” compositions with the later emphasizing the binding of a strand (gathered from a plurality of individual filaments) with other strands at their crossing points (intersection) so as to form mats, fabrics, non-woven or veils and provide strength and dimensional or form stability. Indeed, examination of a fiber mat treated with a binder composition will tend to reveal “beads” of the cured or dehydrated binder composition at or surrounding intersections of adjacent strands throughout the mat. In sizing, the emphasis is on coating substantially the entire surface of each and every filament over its entire length and thereby improving the fiber-interphase-matrix adhesion through physico-chemical interactions. Given the different goals, binder compositions are typically chemically and functionally distinct from sizing compositions that are applied separately to the filaments after they have been coated with a suitable sizing composition.
Additionally, in many sizing compositions, the surfactant package used in the film former emulsion contains low molecular weight compounds which may be unsaturated, have one or more amine groups, or have amino groups which may be characterized as cationic in nature. These compounds will tend to reduce the oxidation resistance of the resulting composition and contribute to degraded composite properties as reflected by, for example, excessive or premature discoloration of the composite part. The low molecular weight compounds include, for example, unsaturated fatty acids and amine based sizing additives and neutralizing agents.
Discoloration of molded composite products, or in the raw materials used to manufacture molded composite products, may be at least partially attributed to contaminants or impurities in one or more of the raw or source materials used to form the composite formulation, or from the presence of contaminants or impurities in the ingredients that are used to form fiber-reinforced composites such as fiber size compositions applied to the reinforcing fibers.
For example, conventional sizing compositions can impart a yellow color or other discoloration to fiber reinforcements coated with such sizing compositions. This discoloration can then be carried over into the composite fiber-reinforced products as the reinforcing fibers are dispersed through the polymeric matrix. Discoloration of the composite products may also be the result of oxidative decomposition of polyolefins or unsaturated compounds, such as surfactants and/or lubricants, which have relatively low thermal stability. Discoloration of the composite products may also be caused by exposure to various nitrogen containing compounds, such as amides, imides, cationic surfactants or amine-based chemicals, which may have been used, for example, as neutralizing agents during production of the polymeric matrix or sizing compositions.
Historically, attempts to suppress or eliminate discoloration have utilized additives such as antioxidants in the composite formulation to counteract or interrupt one or more of the chemical processes that result in the discoloration. Antioxidants are frequently used in the compounding formulations for reducing thermal degradation and associated discoloration during subsequent processing. Other additives include colorants, e.g., a pigment or dye such as TiO2, intended to conceal or counteract the anticipated discoloration of the composite formulation. For example, a blue pigment or dye added to a composite formulation susceptible to yellowing discoloration can produce a composite product that appears to be “whiter.”
More recently, efforts to suppress discoloration of composite products have begun to focus on the use of an optical brightener, such as a fluorescent whitening or brightening agent, added to the composite formulation and/or to the sizing compositions used in forming the reinforced composite products. U.S. Pat. No. 5,646,207, for example, describes a sizing composition that includes a fluorescent whitening agent in addition to other sizing ingredients such as a carboxylated polypropylene, a silane coupling agent, and a lubricant, to reduce the apparent discoloration of the final product. A related patent, U.S. Pat. No. 6,207,737 discloses the use of whitening agents in combination with various stabilizers such as phosphinates, phosphonites, phosphites, hypophosphites, sulfites and bisulfites that are intended to suppress oxidation of the matrix polymer in which the material is used.
Incorporating one or more optical brighteners does not, however, address the underlying discoloration in the molded composite. Indeed, as noted in U.S. Pat. No. 5,646,207, as a result of difficulties in uniformly dispersing the optical brighteners throughout the matrix polymer, discoloration problems can remain in the molded composite product even when a fluorescent whitening agent is incorporated into the composition.
Other technical problems are associated with the use of optical brighteners in both composite formulations and sizing compositions for fiber reinforcements. Technical problems typically include some degradation of the properties of the composite matrix polymer and/or undesirable interactions with one or more of the other composite ingredients. For example, optical brighteners can accelerate degradation of the matrix polymer when it is exposed to ultraviolet (UV) light or other forms of radiant energy. Moreover, optical brighteners themselves can degrade and thus actually contribute to the discoloration of molded composite articles. Similarly, optical brighteners can react with antioxidants, thereby reducing the efficiency of both ingredients, and increasing the likelihood of discoloration. Further, color analysis of molded articles containing optical brighteners is difficult because the brighteners, and hence the molded articles, appear to be different colors under different lighting types and conditions, further complicating efforts to maintain a consistent final color.
Additionally, it has been observed that it is difficult to achieve a sufficient degree of color matching between individual composite batches, particularly when using one or more optical brighteners. In order to compensate for changes in the source materials, varying amounts of selected pigments or other additives can be added to the composite. Because of the number of ingredients contributing to the final color and the potential interaction between various ingredients, it may be very difficult to maintain consistent color between batches of composite material.
The difficulties associated with obtaining composite batches within an acceptable color range will, in turn, increase the overall cost of production by requiring increased quantities of the various starting materials, higher labor costs and increased “scrap” or “rework” material. The use of optical brighteners also contributes to increased production costs simply because the optical brighteners are relatively expensive. Accordingly, each of these technical difficulties poses a corresponding economic disadvantage to efforts to produce a competitive and economical fiber-reinforced composite product.
EP0826710 B1 discloses binder composition using a combination cross-linking accelerators (tetrafluoroborates and/or hypophosphinates) for cross-linking/curing polyacids to form polymeric binder compositions that improve the tear strength of the fiber non-woven veils or mats formed through binding adjacent fibers at their crossover and contact points as well as those regions where the fibers are sufficiently closely spaced to allow for cross-linking of the binder composition between the two adjacent portions of the fibers in nonwoven materials. Although perhaps useful in promoting a cross-linking reaction among the two carboxylic acid groups of the polyacid and hydroxyl or amine compounds, the use of such compounds in compositions apart from binder compositions useful for cross-linking that improve the tear strength of the non-woven veils or mats is not mentioned or suggested.
In U.S. Pat. No. 5,221,285, alkali metal dihydrogenphosphate, and alkali metal salts of phosphorous, hypophosphorous and polyphosphoric acids, are used as catalysts in the esterification (polyester) and crosslinking of cellulose and polycarboxylic acids to form wrinkle resistant fabrics. For example, although sodium tetraborate, boric acid, and sodium borohydride are used to suppress or reduce discoloration resulting from the cross-linking of a cellulosic material with an α-hydroxy acid, there is no teaching or suggestion that such compounds would have any particular utility in a sizing composition to be applied to the surface of forming glass fiber surface and their use as reinforcements in making glass fiber reinforced composites.
Therefore, it is an object of the present invention to provide economical fiber size compositions that maintain or improve the color stability and/or the mechanical properties (particularly as evaluated in both short-term and long term (aged) mechanical properties) for the composite parts. The sizing composition that has been developed to provide this combination of features incorporates an effective amount of one or more of fluorine compounds, boron compounds and/or fluoroborates.
It is an object of the present invention to produce sizing compositions that exhibit improved resistance to discoloration.
It is an object of the present invention to produce sizing compositions that exhibit improved resistance to discoloration without incorporating conventional stabilizers.
It is an object of the present invention to produce sizing compositions that exhibit improved resistance to discoloration by incorporating phosphorus and/or sulfur compounds in which the phosphorus and/or sulfur atoms are in their highest oxidation state.
It is an object of the present invention to produce sizing compositions that exhibit improved resistance to discoloration by incorporating one or more of the boron-, fluorine-, boron-fluorine compounds.
It is an object of the present invention to produce composite articles exhibiting decreased discoloration and provide a method for producing such composite articles.
It is an object of the present invention to produce composite articles exhibiting increased brightness to composite articles incorporating fibers sized or coated with a fiber size composition corresponding to the present invention.
It is an object of the present invention to provide improved color compatibility between composite articles incorporating reinforcing fibers sized or coated with a fiber size composition corresponding to the present invention.
It is an object of the present invention to provide improved whiteness, brightness, and/or color compatibility to composite articles made with fibers sized with the fiber size composition of the present invention without incorporating an optical brightener.
It is an object of the present invention to provide whiteness brightness, and/or color compatibility to composite articles made with fibers sized with the fiber size composition of the present invention without incorporating a conventional antioxidant
It is an object of the present invention to provide whiteness brightness, and/or color compatibility to composite articles made with fibers sized with the fiber size composition of the present invention with no negative (side effects) interactions with the added conventional antioxidant
It is an object of the present invention to provide whiteness brightness, and/or color compatibility to composite articles made with fibers sized with the fiber size composition of the present invention in synergy with a conventional antioxidant
It is an object of the present invention to provide improved whiteness, brightness, and/or color compatibility to composite articles incorporating fibers sized with a fiber size composition according to the present invention while maintaining desirable strength properties of the molded composite article.
It is yet another object of the present invention to provide composite articles made with fibers sized with a fiber size composition according to the present invention that exhibit improved resistance to oxidation degradation.
It is an object of the present invention to provide composite articles made with fibers sized with a fiber size composition of the present invention that resist discoloration.
It is an object of the present invention to provide composite articles made with fibers sized with a fiber size composition according to the present invention that resist thermal degradation.
It is an object of the present invention to provide composite articles made with fibers sized with a fiber size composition according to the present invention that create a stronger interphase between the fiber and matrix resin.
It is an object of the present invention to provide composite articles made with fibers sized with the fiber size composition according to the present invention that exhibit desirable short-term mechanical and aging properties.
It is an object of the present invention to provide composite articles made with fibers sized with a fiber size composition according to the present invention that exhibit long-term aging as well as long-term mechanical properties.
It is another object of the present invention to provide composite articles made with fibers sized with a fiber size composition according to the present invention that exhibits improved resistance to chemical breakdown.
It is an object of the present invention to provide composite articles made with fibers sized with a fiber size composition according to the present invention that exhibits increased resistance to thermal degradation.
The foregoing and other objects, features and advantages of the invention will become apparent from the following disclosure in which one or more preferred embodiments of the invention are described in detail. It is contemplated that variations in procedures may appear to a person skilled in the art without departing from the scope of or sacrificing any of the advantages of the invention.